1. Field of the Invention
This invention relates to a multistage transmission in which a plurality of driving gears and a plurality of driven gears are journaled to mutually parallel gear shafts in a constantly engaged state at every speed.
2. Description of Background Art
In this constant-mesh type multistage transmission, either set of the driving gears or the driven gears is fixed to the gear shaft, the other set is turnably journaled to the gear shaft, and a shift is executed by switching gears fitted to the rotated shaft out of turnable gears by fitting means.
The configuration is known by the present applicant wherein a lost motion mechanism includes shift driving means that executes a shift by switching fitting means which are provided between a plurality of gears and the gear shaft and which fits one gear and the gear shaft for driving the new gear. See, for example, JP Patent No. 2008-246754.
As for the shift driving means of the multistage transmission disclosed in JP Patent No. 2008-246754, a control rod arranged along a central axis of a hollow part of the gear shaft is slidingly touched inside four types of cam rods axially movably slidingly touched to an inside periphery of the hollow gear shaft. Lost motion mechanisms are laterally arranged inside the four types of cam rods with each lost motion mechanism being coupled to the required cam rod.
In the lost motion mechanism, a spring that axially acts is inserted between the control rod and each cam rod for interlock and the lost motion mechanism is housed in the hollow part of the gear shaft.
When the control rod is moved for a shift, the fitting means, the fitting of which is previously maintained, is naturally released by this lost motion mechanism in transition from a state in which the fitting before the shift by the fitting means is maintained to a state of fitting after the shift by the fitting means. Thus, a smooth transition is enabled, and shifts are smoothly executed without discontinuation.
An upward shift in acceleration and a downward shift in deceleration are smoothly executed as described above. However, in a downward shift in acceleration and an upward shift in deceleration, as the fitting means the fitting of which is maintained before the shift is not naturally released, the shift cannot be executed without any means.
However, as the control rod is moved by the lost motion mechanism though the shift cannot be executed, a driver (a rider) who operates the shift has a sense of incompatibility for a situation wherein the shift is disenabled though the operation is enabled.
When the control rod is moved by turning a shift drum by a predetermined angle by operation for a shift and the shift is executed, fitting by fitting means before the shift is maintained till fitting by fitting means after the shift by the lost motion mechanism, the fitting by the fitting means before the shift is smoothly released by the fitting by the fitting means after the shift, and shifts are smoothly executed without discontinuation.
As the fitting by the fitting means before the shift is maintained till the fitting by the fitting means after the shift, the shift drum is turned when operation for the next shift is executed before the fitting by the fitting means before the shift is released, a spring of the lost motion mechanism is further compressed, the control rod is moved, a state in which the fitting means after the shift is made fittable is released because of the further movement of the control rod, the fitting by the fitting means before the shift cannot be finally released, and the shift is disenabled.
Nevertheless, as the shift drum is turned, a situation wherein a shift position of the shift drum and the actual speed are not matched occurs.